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Celuaris SPK5 Purifi Review (speaker)

amirm

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This is a second review and detailed measurements of Purifi woofer reference design implementation by Celuaris called SPK5. The original sample had some enclosure leakage issues which have been resolved in this unit due to collaboration between our DIY expert, @Rick Sykora, and builder, @sgoldwin.

I am going to borrow the picture from the last review since nothing is changed in that regard:

index.php


The crossover is now built inside the unit rather using the external one in the previous reference design.

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in ordinary rooms yet results that can be more accurate than an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

I performed over 1000 measurement which resulted in error rate of around 1%.

Temperature was 58 degrees F at sea level. I kept the speaker indoor at 70 degrees prior to starting the measurements.

Measurements are compliant with latest speaker research into what can predict the speaker preference and is standardized in CEA/CTA-2034 ANSI specifications. Likewise listening tests are performed per research that shows mono listening is much more revealing of differences between speakers than stereo or multichannel.

Reference axis was the tweeter center which in case of these AMT tweeters is a bit inexact.

Celuaris SPK5 Purifi Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker is and how it can be used in a room. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:

Celuaris SPK5 Purifi Measurements Spinorama CEA-2034 Frequency Response.png


Compared to the first sample, bass extends lower but it starts to droop starting at 100 Hz. We have a dip around 350 Hz which is caused by port resonance:

Celuaris SPK5 Purifi Measurements driver frequency response.png


I am disappointed in the uneven response of the tweeter which has at least one resonance which showed up in the spin graph above.

Early window is fine other than showing that the tweeter due to being narrow width-wise, is starting to "beam" (narrow its radiation angle:

Celuaris SPK5 Purifi Measurements Spinorama CEA-2034 early window Frequency Response.png


We see that just the same in our predicted in-room response:

Celuaris SPK5 Purifi Measurements Spinorama CEA-2034 Frequency Response predicted in-room resp...png


The main claim to fame of Purifi driver is low distortion -- something we did not see in the first sample I tested. Fortunately here it becomes the star with strong showing:

Celuaris SPK5 Purifi Measurements relative distortion.png


Celuaris SPK5 Purifi Measurements THD distortion.png


It is so good that it makes the tweeter really look bad.

Horizontal directivity now is much smoother:
Celuaris SPK5 Purifi Measurements horizontal beam width.png


Celuaris SPK5 Purifi Measurements horizontal directivity.png


Here is our vertical:

Celuaris SPK5 Purifi Measurements Vertical directivity.png


Finally, the impedance and phase:
Celuaris SPK5 Purifi Measurements impedance and phase.png


Celuaris SPK5 Purifi Speaker Listening Tests
The sample speaker I have has SpeakOn connector and the only cord I had for it did not extend long enough to test the unit where I normally do. So I had to move the speaker to the right side of my room where there is no bass enhancement. Whether it was that or something else, the results were quite unsatisfying. There was not a whole lot of bass at normal playback levels. Due to low efficiency, I had to push the speaker hard to get bass out of it but then the winding would suddenly jump the gap and cause nasty static. Tracks with deep bass didn't distort the speaker but they were hardly played down low either. I played around a bit with EQ but didn't get far so gave up.

To make sure the new location or my mood was not at fault, I replace the SPK5 with Revel M106 and boy what joy there was with that speaker. Thundering and clean bass was back as was warm tonality. I could detect no more distortion there than I did in SPK5.

Conclusions
If this were a test of distortion for the Purifi driver, mission is accomplished. This is one low distortion driver. Alas, the reference design that Purifi has created is not optimal. The tweeter I feel is not the right match nor is the enclosure to get proper bass and efficiency here. I am not sure of the purpose of a fancy driver if you don't have much bass and you have low efficiency to boot. Objectively the results look better than my impression so perhaps I am being too harsh. I don't know.

As is, I can't recommend SPK5. Feel bad saying that despite the heroic efforts of its builder who went through some five (5) samples to get us to this point with transatlantic shipping issues, samples getting lost, etc.

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As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

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  • Celuaris SPK5 Purifi spinorama.zip
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YSC

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I wonder if someone like Adam, genelec or Neumann adopted these drivers they might produce something more amazing.

side note: any reason the tweeter is located on the side rather than in the middle?
 

Doodski

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What is the expense for this speaker? How much does a pair cost?
 

MZKM

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What is the expense for this speaker? How much does a pair cost?
It’s a concept design from Purifi to showcase to manufactuers. The member here uses the public plans to build them, and it’s ~£2000, mainly due to the tweeter costing ~$900/pair and the woofers costing ~$700/pair (these are not using bulk discounts).

I speculated before, but I really think they went with this underwhelming tweeter (for the money), because it is an AMT and it’s expensive. So, it is meant to showcase that it can be crossed over quite high (>3kHz) without much detriment and that is belongs in exotic/expensive setups.

No knock to the member who sells them, as he is just following plans and meeting demands for those that want it, but for a similar price, Rick (Selah Audio) sells their Purezza, which is a 2-way bookshelf using this woofer with a ribbon/planar tweeter that is much better (with a cabinet that looks professional), Erin measured them, and he liked them more than Dennis’ BMR If I recall (which just goes to show how great the BMR is, getting compared to a speaker >1.5x more expensive):
https://www.erinsaudiocorner.com/loudspeakers/selah_audio_purezza/
 
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Doodski

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He is showing the cost at £1,999 ($2,700) but I am not sure if it is a pair or not. I think it is.
That's a lotta bucks for those speakers. USD $2700.00 could buy some pretty nice factory made speakers but I guess that defeats the DIY MODDER mentality.
 

MZKM

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side note: any reason the tweeter is located on the side rather than in the middle?
Some manufacturers do this. From what I can gather, centered will give you the same frequency of cabinet diffraction for the side edges, off-set will have different frequencies (different distances from side edges).

So, if you don’t want to go crazy with the crossover in dealing with a large peak, you off-set it so that while you do get 2 peaks, they are of less intensity than the single peak.
 

YSC

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Some manufacturers do this. From what I can gather, centered will give you the same frequency of cabinet diffraction for the side edges, off-set will have different frequencies (different distances from side edges).

So, if you don’t want to go crazy with the crossover in dealing with a large peak, you off-set it so that while you do get 2 peaks, they are of less intensity than the single peak.
Ic, but then would it be better when in a pair have different side offset so the image is more balanced?
 

pio

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tktran303

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Amir,

Thanks for the measurements.

Confirms that the other sample was broken
(https://www.audiosciencereview.com/...ker-review-prototype.17806/page-3#post-578524)

The midwoofer itself is low distortion unit, yes, but the cabinet alignment (vented @ 30Hz for 1/2 cu ft) is just too low IMHO. This is why the bass droops off below 100Hz.

So it sounds like it’s missing bass because there’s so much musical content between 40-100Hz, and not that much between 20-40Hz.

If I was designing for 1/2 ft I’d design for a port tuning at 40Hz.

And the tweeter selection is puzzling to me.

I wonder why the designer chose this treble unit?

This midwoofer is well behaved and can be crossed over to any number dome tweeters (with or without waveguide) at/under 2Khz or ribbon tweeters around 3Khz.

I, too, agree that Rick Craig's Purezza
http://www.selahaudio.com/purezza
is a more refined design than this in-house engineering design/prototype...
 
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dfuller

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I wonder if @Rick Sykora 's experiment with a passive radiator with provide some interesting results that would deal with that port cancellation.
 

ROOSKIE

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I wonder if @Rick Sykora 's experiment with a passive radiator with provide some interesting results that would deal with that port cancellation.
That port is long which drives the main port resonance down into a frequency range where the stuffing in the enclosure (if it uses some) will not absorb/reduce the frequency of the resonance much if at all.
There are several ways to design a port with out a strong 1st resonance but the easiest is to drive that resonance higher so stuffing affects it, but that requires a tuning that use a shorter port length.
If you can drive it up toward the 900-1100hrz zone then stuffing can really reduce the resonance peak.
I believe that the JBL 708p speaker recently tested does not have stuffing so in that speaker that 900hrz resonance is still strong, had it been stuffed it may have been 10-15db down.
In any case you can end up with a passive radiator resonance as well - no completely free lunch. You do not get port chuffing (obviously with no port) but the passive radiator still can have issues that a sealed design does not. The sealed designs also have their benefits, they also have some detriments. It is all give and take.
In any case I have to agree with @tktran303 that this design is just not impressive as showcase for this woofer & that the tweeter selection continues to seem absurd even if one is being nice about it all. It comes off as DIY project about at my level which is "competent enough to know not to send my design in to ASR anytime soon, DIY hack at best."
Still though it rings up a Harman score of 5.8 so that messes with my mind a bit.
 
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YSC

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I am thinking what could one do making it active so the active crossover maybe can do it even better with a normal tweeter?
 

Beershaun

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This is why it's so great to have measurements. I'm sure the builder values them as much as we do so they know where they can improve their design. That woofer response from 100-2k is super smooth. That and the low distortion shows there is some good stuff in there. The port and tweeter let it down. Maybe better served as a mid range in a 3 way setup and a different tweeter.
 

Juhazi

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Some manufacturers do this. From what I can gather, centered will give you the same frequency of cabinet diffraction for the side edges, off-set will have different frequencies (different distances from side edges).

So, if you don’t want to go crazy with the crossover in dealing with a large peak, you off-set it so that while you do get 2 peaks, they are of less intensity than the single peak.

Sometimes offset will make left/right off-axis response different, but not in this case

tweeter midline  offax edge.jpg
 

uwotm8

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Way too expensive for such results IMO. I believe that many of more traditional kits/combinations (ScanSpeak or Seas-based) will afford a better performance within the same driver pack budget. A little LF distortion with actual LF is far better than lower distortion without bass:p

But yes, with Purifi you get that alien organics looking suspension. May be important tho.
 
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